Field of Invention
This invention relates to a novel data management method and system for random access electron beam memories.
More particularly, the invention relates to such methods and systems for use with electron beam memories employed as main or peripheral memories in high speed digital computing systems.
Background Problem
In electron beam memories in which memory access for either storage or readout purposes is by means of an electron beam, the number of accesses to a given physical location on the recording member must be limited in order to avoid deleterious physical changes (fatigue) induced by the electron beam into the memory medium. A related problem arises because the average time distribution of accesses, i.e. the average rate of access, may need to be restricted in order to provide sufficient time between accesses (or between a group of repetitive accesses) to allow the recording medium to recover after electron-beam bombardment. For such electron beam memories, it is desirable therefor that for a given total number of accesses to the memory, that both the least number of accesses to any particular location and the lowest rate of accessing be simultaneously achieved by uniform access, i.e., all other addresses are accessed before reaccessing a given address.
Conventional terminology uses the term random access to mean unrestricted access. Mathematically, random access defines access to any address as equally probable on each and every access to memory. In most data processing systems, however, after access to a given address, the next address is not on the average chosen at random. For example, there may be a higher than 50% probability that this same address will be addressed again either immediately or shortly thereafter. An extreme example occurs in the case of completely repetitive accessing of a single address. Another common situation that might arise is that addresses follow each other sequentially, which is an example of uniform addressing, i.e., all other addresses are accessed before reaccessing a given address.
From the foregoing discussion, it will be appreciated that with respect to electron beam accessible memories a need for a data management method and system such that unrestricted accessing from the programmers point of view can be made to approach uniform accessing from the hardware point of view. To provide such a method and system, the present invention was devised.